1. Field of the Invention
The present invention relates to an electronic scanning radar apparatus, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program. More particularly, the present invention relates to an electronic scanning radar apparatus being preferable to be equipped in a moving body, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program, in which the electronic scanning radar apparatus transmits a transmission wave to a target so as to detect the target by receiving a reflection wave of the transmission wave reflected from the target.
Priority is claimed on Japanese Patent Application No. 2009-296081, filed Dec. 25, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In general, an electronic scanning radar apparatus is known as radar to be equipped for a moving body. For such radar, a frequency modulated continuous wave (FMCW) radar, multiple-frequency continuous wave radar, pulse radar or the like is employed.
For each radar described above, a receiving wave direction estimating method with array antennas is used for detecting the direction of a receiving wave from a target. The receiving wave may be referred to as an incoming wave, and the target may be referred to as a reflecting object.
Recently, the receiving wave direction estimating method employs highly accurate algorithms such as an auto regressive spectral estimation method (AR spectral estimation method; see FIG. 34), a multiple signal classification method (MUSIC method) or the like, which can provide high resolution (high accuracy) of the direction of receiving waves without increasing channels of receiving antennas. These methods are described in Japanese Unexamined Patent Application, First Publication, Nos. 2006-275840, 2007-40806 and 2009-156582, and also described in “MATLAB Multi-media Signal Processing part I: Digital signal fundamentals” published by Ikehara and Shimamura in 2004 by BAIFUKAN CO., LTD., and also described in “Adaptive Signal Processing with Array Antennas” published by Kikuma in 1998 by Kagaku Shuppan Co. LTD.
The AR spectral estimation method is also referred to as a maximum entropy method (MEM) or a linear prediction method.
For estimating the direction of receiving waves from a target (reflecting object) with those algorithms, input data indicated by complex numbers are converted into a matrix form called as a correlation matrix, and then the estimation process is performed.
Furthermore, in the receiving wave direction estimating method equipped in a moving body, a detecting process is repeatedly performed in detecting cycles (control cycles). Correlation matrixes obtained in previous (past) detecting cycles are stored in a memory (or a data storage device) as past correlation matrixes so that an averaging (or addition) process is performed between the present correlation matrix obtained by the present (latest) detecting cycle and the past correlation matrixes. Thereby, the direction estimation process is performed. See Japanese Unexamined Patent Application, First Publication, Nos. 2007-40806 and 2009-156582. This averaging process of the correlation matrixes can reduce noise factors, so that the accuracy of the receiving wave direction estimation is improved.
When a number of channels used for an array process is decreased, the accuracy of the estimation is reduced even if a highly accurate algorithm is used, because the number of data sets (data) becomes insufficient for an accurate estimation. Namely, when the number of data sets becomes insufficient, it becomes difficult to treat the receiving signals as ideal sine waves. This influences the results of correlation processes. For this problem, it is expected to obtain significant effects for improving the accuracy of the detection of the target by performing the averaging process between the correlation matrixes.
Japanese Unexamined Patent Application, First Publication, No. 2007-40806, describes that the correlation matrixes must be stored in the memory (or storage device) as information that corresponds to the whole distance (frequency) points. This requires a mass storage device (or large capacity memory) when the detection range is expanded or the detection accuracy is improved. The past correlation matrixes have beat frequencies that correspond to those of the present correlation matrix. This condition provides proper averages for detecting the direction of the target as long as the electronic scanning radar apparatus follows the target with a constant distance. However, when the distance between the electronic scanning radar apparatus and the target is varied, there is a possibility that the beat frequency of the present correlation matrix does not correspond to those of the past correlation matrixes. This could degrade the data used for detecting the direction of the target.
The present invention takes into consideration the issues described above. One of the objects of this invention is to provide an electronic scanning radar apparatus, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program, which make it possible to accurately detect the direction of receiving (incoming) waves from the target while maintaining the accuracy of the signal detections.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses the need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.